1. Field of the Invention
The present invention relates to an x-ray microfilm reader in which a magnified x-ray image from a frame of microfilm is projected onto an image plane for viewing by a user or for recording on a photosensitive film.
2. Description of the Prior Art
Microfilm storage of information has found wide use in businesses, libraries, and other establishments where cost and physical space constraints prevent the storage of original documents. Microfilm has also found use in hospitals and clinics for the recording of x-ray images. This is very advantageous, since the original x-rays are large and are inconvenient to store and retrieve if needed later.
One commonly used type of microfilm system for recording x-ray images uses strips of 35 mm microfilm which are stored in plastic jackets. This type of system, however, has several significant disadvantages. First, the individual jackets containing film can become missorted, misplaced, or lost. Second, because viewing is through the plastic jackets, artifacts or "rainbows" can be created which can, in some cases, affect or change the physician's diagnosis.
An improved microfilm format for use in recording x-ray images uses a roll of microfilm which is stored in a cartridge. For example, Minnesota Mining and Manufacturing ("3M") sells a square cartridge which is designed to hold 16 mm microfilms. In this format, none of the images on the long web of microfilm can be lost unless the entire cartridge is lost. Similarly, images cannot be missorted or misfiled unless the entire cartridge is lost. In a typical clinic or hospital operation, all cartridges of x-ray microfilm are kept under a common control in a central location. No one is allowed to take the original cartridge from that location. A microfilm reader is provided to allow personnel to view the images stored on the microfilm.
Any microfilm system, of course, requires a microfilm reader, since the images that are recorded are too small to interpret without being magnified. One type of microfilm reader which has been used in the past includes a hook which attaches onto the microfilm. The drive system for this reader uses the hook to pull the film through the film track.
Another type of microfilm reader uses a drive roller to drive a leader (which is attached to the leading end of the microfilm) through the film track to a takeup reel which is driven by a drive motor. Once the film leader has reached the takeup reel, the takeup reel pulls the leader and attached microfilm through the film track. Rewinding is provided by driving the spindle on which the film is stored in a reverse direction, thus pulling the film out of the film track back onto the spindle.
In the past, the controls for microfilm readers have typically been manual rather than automatic. Controls have typically included a display which indicates a frame number which is incremented or decremented as the microfilm is moved. The user can locate a particular frame by controlling the drive until the correct frame number is displayed. Microfilm readers have typically used three sensors located above the film gate to sense the frame location holes in the microfilm. A center sensor is used to control the frame location, while the sensors on either side of the center sensor indicate the direction in which the film is traveling. These systems have often suffered from undershoot or overshoot of the image, which then requires adjustment so that the frame is centered in the film gate (and thus is centered on the projection screen).
There is a continuing need for simpler, easier-to-use microfilm readers, particularly in the field of x-ray microfilm readers. In particular, there is a continuing need for an improved x-ray microfilm reader which not only provides automatic loading, unloading, and frame searching, but also provides high quality reproduction of the x-ray image, so that the physician can obtain a full-size x-ray transparency for more detailed examination.